1. Field
The present invention relates generally to the control of light incident to imaging devices, and may be applied, for example, to portal imaging in conjunction with radiation therapy.
2. Description
Many types of conventional imaging devices create image data based on light incident thereto. Known charge-coupled devices and amorphous silicon devices convert incident light to stored electrical charge. For example, a photodiode of an amorphous silicon imaging device accumulates electrical charge in proportion to an intensity of received light. After a specified time period, the accumulated charge is read in order to calculate the intensity of light received by the photodiode.
It may be desirable to operate an imaging device within a particular range of light intensities. This particular operating range is often associated with a maximum signal-to-noise ratio of the imaging elements of the imaging device. More particularly, the imaging elements of an imaging device may most accurately detect differences in the intensities of incident light in a case that the intensities fall within the particular operating range.
An imaging device may be susceptible to saturation. Saturation describes a situation in which one or more imaging elements of the imaging device is unable to respond to additional incident light. With respect to the aforementioned charge-coupled devices and amorphous silicon devices, saturation exists in a case that an imaging element cannot store additional electrical charge even if the imaging element receives additional light. An imaging device cannot accurately detect relative differences in the intensity of light incident to various imaging elements of the imaging device if one or more of the various imaging elements are saturated.
An imaging device may be designed and/or calibrated to perform an imaging task in view of the foregoing considerations. This design/calibration attempts to ensure that light intensities associated with the imaging task fall within a high signal-to-noise operating range of the imaging device and would not cause any imaging elements to saturate. However, various imaging tasks may present conflicting ranges of light intensities. As a result, an imaging device that is designed and/or calibrated for a first imaging task may experience a low signal-to-noise ratio and/or saturation if used for a second imaging task.